Muscular dystrophy refers to a group of genetic, hereditary muscle diseases and disorders that cause progressive muscle weakness. These diseases and disorders are characterized by progressive skeletal muscle weakness, defects in muscle proteins, and the death of muscle cells and tissue. Many different diseases including Duchenne, Becker, limb girdle, congenital, facioscapulohumeral, myotonic, oculopharyngeal, distal, and Emery-Dreifuss are classified as muscular dystrophies.
Duchenne muscular dystrophy is the most common form of muscular dystrophy and primarily affects boys.
Mutations of the membrane-associated proteins dystrophin and merosin result in progressive muscle wasting and weakness in Duchenne and congenital muscular dystrophy, respectively (Dalkilic, 2003; Tidball, 2005). Boys with Becker muscular dystrophy (very similar to but less severe than Duchenne muscular dystrophy) have faulty or diminished amount of dystrophin. Following muscle plasma membrane damage during contraction, muscle injury produces dysregulation of a broad spectrum of structural and regulatory genes which accompany muscle fiber death (Petrol et al., 1993; Tidball, 2005; Ge et al., 2004). Interestingly, while initial even severe muscle degeneration results in extremely effective regeneration in cases of rhabdomyolysis, recurrent muscle injury in muscular dystrophy is associated with failure of regeneration and replacement of the muscle tissue with fibrous tissue (fibrosis) and fat.
The laboratory of the present inventor is interested in the pathophysiology of muscular dystrophy and the inter-relationship and interaction between fibrosis and regeneration in these muscular dystrophies (Nevo et al., 2006; Biton et al., 2006) and looks for the development and implementation of therapeutic modalities that will inhibit muscle inflammation and fibrosis and enhance regeneration in muscular dystrophy patients.
Inflammation in Muscular Dystrophy
Inflammatory process plays a major role in promoting the pathology of dystrophin-deficient muscle (Morrison et al., 2005). The degeneration of muscle fibers is accompanied by invasion of inflammatory cells including macrophages, CD4+ and CD8+, T lymphocytes, IgG, IgM, and eosinophils (Spencer et al., 2001). In the mdx mouse model, T cells are reported to contribute significantly to apoptosis of skeletal muscle and progressive fibrinogenesis during repeated cycles of muscle degeneration (Morrison et al., 2000; Spencer et al., 2001). Mdx lymph node cells produced large amounts of INF-γ but not IL-4, IL-6 or IL-10 after in vitro mitogen stimulation with concanavalin A, especially during the regeneration phase of muscular dystrophy. INF-γ is a cytokine that up-regulates the expression of adhesion molecules, major histocompatibility complex (MHC) gene products and chemokines, which can ultimately stimulate an inflammatory reaction occurring in the muscle tissue (Matthys et al., 1999, 2001; Tran et al., 2000). However it is possible that INF-γ is also playing a protective role in the control of skeletal muscle inflammation and fibrosis in the mdx mice. INF-γ also participates as a direct B-cell-maturing cytokine, driving normal B cell to active Ig secretion.
In the mdx mice, depletion of macrophages prevents most muscle membrane lysis at the peak of pathology (Wehling et al., 2001). Implication for the participation of T cells in the process of fibrosis was demonstrated in experiments carried out in mdx mice with the nu/nu background. Transplantation of normal thymic tissue into mdx nu/nu mice replenished deposition of altered collagen in the muscular tissue comparable to wild-type mdx dystrophic mice (Morrison et al., 2000).
Copolymer 1—Glatiramer Acetate (GA)
Copolymer 1, first described in U.S. Pat. No. 3,849,550, is an FDA and Israel Ministry of Health approved drug for multiple sclerosis (MS) that slows the progression of disability and reduces relapse rate while exhibiting a very high safety profile. MS and its animal model, experimental autoimmune encephalitis (EAE), are inflammatory autoimmune diseases of the central nervous system (CNS) characterized by myelin destruction and axonal damage. Glatiramer acetate (GA), the trivial chemical name for the acetate salt of Copolymer 1, is composed of the amino acids L-alanine, L-lysine, L-glutamic acid, and L-tyrosine in a molar ratio of 4.2:3.4:1.4:1.0, and is marketed under the name Copaxone® (a trademark of Teva Pharmaceutical Industries Ltd., Petach Tikva, Israel). It was designed to simulate myelin basic protein (MBP). The immunological cross-reactivity with MBP was initially considered the cause for its activity.
Copolymer 1 and T cells activated thereby were also found to confer neuroprotection and to inhibit secondary neuronal degeneration caused by an injury, disease or disorder in the CNS and to protect CNS cells from glutamate toxicity (WO 01/52878, WO 01/93893, U.S. Pat. No. 6,844,314). In this context, Copolymer 1 was found to confer neuroprotection in animal models of amyotrophic lateral sclerosis (ALS) (WO 03/047500), Parkinson's disease and Alzheimer's disease (WO 2005/046719). Treatment with Cop 1 by ingestion or inhalation is disclosed in U.S. Pat. No. 6,214,791 and by eyedrops in WO 2004/060265.
GA exerts its therapeutic activity by immunomodulating various levels of the immune response, which differ in their degree of specificity. The prerequisite step is the binding of GA to MI-IC class II molecules. GA exhibited a very rapid, high, and efficient binding to various MI-IC class II molecules on murine and human antigen-presenting cells, and even displaced peptides from the MHC-binding site. This competition for binding to the MI-IC can consequently lead to inhibition of various pathological effector functions. It was shown that GA promotes T helper 2 (Th2) cell development and increase IL-10 production. This modulation on the level of antigen-presenting cells is the least specific step and can be beneficial for the modulation of detrimental immune responses to various antigens. (Aharoni et al., 1999, Putheti et al., 2003, Farina et al., 2005).
GA-immunomodulating activity is not limited to the brain. GA-induced Th2 regulatory cells were demonstrated in other organs (spleens and lymph nodes of experimental animals and peripheral blood mononuclear cells in humans). Moreover, as demonstrated in these studies, highly reactive GA-specific T cell lines secrete in vitro IL-4, IL-5, IL-10, and TGF-β in response to GA (Miller et al., 1998). In skin transplantation system, GA significantly prevented skin graft rejection. GA alleviates immune rejection and drastically reduced cytotoxic activity toward host targets in bone marrow transplantation (Aharoni et al., 1997; 2001).
Muscular dystrophy is not a primary inflammatory disorder. However, as previously shown the process of replacement of the normal muscle tissue by fibrosis in muscular dystrophy is mediated and enhanced by inflammation. There is no previous data on the effect of Copolymer 1 on muscular dystrophy.
Current Treatment of Muscular Dystrophy:
Corticosteroids are the only available medication with proven efficacy in Duchenne muscular dystrophy (DMD). In the short-term, corticosteroids significantly improve muscle strength and function in DMD (Manzur et al., 2004). Long-term corticosteroid treatment is associated with clinical benefit of improvement in muscle strength both in the mdx mice and in boys with DMD, prolonging their shortened lifespan and amelioration of scoliosis (Keeling et al., 2007). However, prolonged corticosteroid treatment is associated with severe side effects including obesity, hypertension, cataracts, bone fragility, behavior disturbances and others (Angelini, 2007). The mechanism of action of corticosteroids in muscular dystrophy is not entirely known. Corticosteroids have significant anti-inflammatory and immune modulation effect. Treatment of patients with dystrophies with corticosteroids reduces the mononuclear inflammatory cells (MICs), (Hussein et al., 2006) and the total T cells number (Kissel et al., 1993).
It would be highly desirable to provide medicaments for the treatment of DMD and other non-DMD muscular dystrophies for which no medication is presently available.